The compression strength of a corrugated box is a direct measure of the stacking strength of corrugated board packages. However, since the load-bearing properties of a box are often of decisive importance under modern transport conditions, it can also be said that the compression strength constitutes a general measure of the performance potential of a corrugated board package. The compression strength is measured according to a standardized test method and is in general designated the BCT (Box Compression Test) value.
The BCT method is a pure top to bottom load test which is, as a rule, carried out on empty sealed corrugated board boxes which are compressed between flat parallel plates in a compression tester at a constant compression rate. The rate is usually between 10 and 13 mm/min. The force and strain are recorded continuously until a compressive failure occurs. The maximum force attained is reported as the compression strength of the corrugated box. The test is carried out in a standardized atmosphere of 23 degrees Celsius and 50 percent relative humidity.
The method is generally acknowledged to be that which best corresponds to practical performance in the stacking of corrugated board boxes. The BCT method has also shown itself to be a good method of comparing the load bearing capabilities of different corrugated board boxes. The boxes must however be of the same size for the comparison to be valid.
Knowledge of the compression strength of a particular corrugated box has many useful purposes. The BCT value will determine how many boxes can safely be stacked on top of each other in warehouse or on a truck. If a greater density of boxes is required in a stack in order to best fill out a truck or storage area than the BCT value must be increased. This is accomplished by either changing the design of the corrugated box or strengthening the board used in its construction.
The box compression test gives the package designer a useful tool to help determine the proper corrugated board grade to use in order to meet the demands required for the box. This will insure that the box will be able to fulfill its intended use. The BCT test will reduce damage to products and waste of packaging material, because the corrugated box will be designed to surpass the minimum requirements.